By default, LeCoach automatically updates your FTP whenever you update your FTP in Intervals. This also goes for other data fields such as your Vo2max, power zones, hr zones, max hr, threshold hr etc. In other words, whenever something changes in Intervals this also changes in LeCoach.
You can however also select to treat these fields as manual. This means for example that you overrule the FTP field coming from Intervals with your own FTP field. This could be useful if you want to work with a static or more controlled number for FTP if the value changes frequently in Intervals.