The shared context of a task sounds like a pure benefit: the more a session knows about the project, the less you have to explain. Spaces in Devin Desktop give exactly that - and that is exactly why a Space is easy to turn from a tool into a dump. A Space unites sessions, PRs, relevant files and project context, and a new session inside it inherits the accumulated knowledge. As long as you see only the saving of explanations in this, you miss the other half: everything in the Space is inherited, including its mistakes.
The naive move is direct: since inheritance is convenient, pile all sessions into one shared Space so that each one knows everything about everything. It seems that this way the agent will never be in the dark and questions will drop away by themselves. The tool encourages it - sessions group easily - and for a while it feels as if the wider the shared context, the smarter the agent.
It breaks on the nature of context: context is not only facts but also everything else that landed in it. The documentation describes a Space as a union of sessions, PRs, files and project context inherited by new sessions, and the important detail is that each session is already its own Space by default. So there is no need to build shared spaces in advance; grouping arises as work proceeds. And since the whole shared context is inherited, a disputed hypothesis written down as a fact is inherited on a par with a verified decision.
The professional mechanism here is to group deliberately and keep the contents clean. Inheritance is governed by the devin.spaces.shareContext setting: a new session takes the Space's context when it is on. You can assemble a Space in several ways - drag one session onto another in the sidebar to merge them into a shared space; press Cmd/Ctrl+\ to split and start a new session in the blank area; open a fresh session within the current Space with Cmd/Ctrl+T. But the mere fact that grouping is easy does not mean everything should be grouped.
Why you should group only related branches of one goal, not everything at once. A Space is useful exactly to the extent that its shared context is relevant to every session in it. Two tasks about one subsystem gain from shared knowledge; two unrelated tasks in one Space merely share with each other the noise that neither of them needs. Shared context is an amplifier: it amplifies the useful and the harmful alike.
The cost of ignoring the cleanliness of context is concrete: shared context gets polluted the way any shared resource does. A disputed hypothesis added as a fact will be inherited by all new sessions of the Space, which will act as though it were proven. A stale decision not removed after a change of direction will keep leading the agent down the old path. The wider the Space, the more expensive such a mistake, because it is replicated across all inheritors at once. It is cheaper to keep it clean continuously than to scrub, once, a shared context several sessions have already relied on.
A shared Space is justified where several sessions truly have one goal and shared knowledge of it saves repetition. The sign of such a situation is that you can name in one sentence what this Space serves and why each of its sessions belongs in it. If no such sentence is found, what you have is not a Space but a warehouse of assorted chats that happened to end up side by side.
You should judge a Space's health by its pinned contents, not by the number of sessions. Into the shared context you pin what is verified and useful to all: acceptance criteria, accepted decisions, links to artifacts. From it you remove the stale after each change of direction. A healthy Space reads like a short map of the task; a sick one, like a chat history in which fact cannot be told from guess.
Hence an engineering technique: treat shared context more strictly than a personal note, not more loosely. In a personal session an inaccuracy costs you alone; in a Space it costs every inheriting session. So the disputed is marked as disputed or not put into the shared context at all, and decisions and criteria are phrased so they can be checked, not merely read. This is a technique of discipline, not a product feature: the system stores what it was given, the value of the contents is on you. A practical test is simple: reading only the Space's pinned context, an outsider should understand the task and take not a single guess for an established fact.
The typical failure is one giant Space into which everything flows, and a hypothesis written down as a fact. The symptom is easy to recognize: new sessions start with confident statements no one has checked, and it is no longer possible to find where an assumption came from. Before widening a Space, ask whether all of its sessions serve one goal and whether the shared context holds the unproven as proven - most often the mess is there, not in the agent.