berthstein:
Yes, it is.
If you want to apply a patch to your phone, add it in the "misc" tab in SE Tool lite and accidentally press "Write GDFS" instead of "Write Script" your phone will be a brick. That may sound stupid but it happened to many users.
If you haven't got a model which is supported by SEMC8.4 or SET2cracked you won't be able flash any other GDFS and restore the important values so that the foreign GDFS will work for your phone.
It's even worse if you screw up the GDFS of a DB2020 phone (from now on you'll need SE Tool 3 Box). Those are really hard to fix. If you've got a CID52 phone you won't be able to format the GDFS area. If there is any trash data you won't be able to revive the phone.
If you've got a CID49/51 phone you can read out the secunits, flash a foreign GDFS and restore the secunits backup. That won't work out if these values have already been altered.