I use exclusive locks where multiple processes concur for data access, and these locks guarantee the data consistency.

For example, the GUI engine may eventually start cleaning its old cache, and the exclusive lock prevents other GUI processes (which are mod_perl or fcgi processes) to do the same.

another example is when the database is big enough, and when multiple collector processes start at the same time, I use the exclusive lock to let them initialize and slurp the data sequentially: this prevents from excessive disk seeks.

but as you mentioned in another thread, your solution is locked to a single architecture, and I cannot afford that.