What is Claude's "projects" feature and how can it be used for client-specific work?

Projects let you set up a dedicated space (similar to Perplexity's "spaces") where you drag in reference files, presentations, or writing samples so Claude has consistent context — background, voice, tools used, and beliefs — for a specific ongoing purpose. Claude itself can help write the setup instructions and pick which files should live in the project. Every new chat inside a project automatically pulls from those stored files, so you don't have to re-explain context each time. One use case described was a 12-month coaching program for six accounting firms: dumping in call transcripts, financials, intake forms, client lists, and pricing each month, then asking Claude for the top three things the firm should focus on next, or asking it to build a resource for a specific issue. Projects were suggested as potentially very useful for tax planning or maintaining a project per client. Within a project, there are also settings for effort level (e.g., extra/max reasoning for Opus 4.5, which is slower but intended to give the best answer) and "skills" you can drop in to change output style, including a research-report style output. The advice given was to keep each chat focused on one topic rather than one long running chat, since long chats can get "lazier" over time.