To isolate changes for one feature or one developer, you can create a branch for each feature or developer. In this way, the developers are working on their own branches, with no conflicts with others until they hit a point when their work is done, and they then integrate the changes back into the master branch.

After the feature is finished and integrated back to the master branch, the feature branch can be deleted. If the branch is per developer, you can expect that the branch will live a long time. This could be a problem from a long-term point of view. The following diagram depicts this:

Using one branch per developer will mix different changes for different features together, and it could be a problem to release only selected features later in the process.

Using branches per feature gives you the possibility to release only selected features or cancel feature development for no cost (before it is integrated back into the master branch).