Workspaces in regions far from where the users work.

Do I need to create workspaces close to where the users work? I saw a table that listed "fast", "medium", "slow" etc. for latency between regions. But I can't find the table, and I didn't bookmark it! Can you point me to the table? I was surprised that London/N. Virginia was labeled "Fast." For a very simple setup, is it ok to reach across the Atlantic to your workspace?

Thanks!