For me there is little in the way of a disadvantage in moving a file to the chest. There is however a major disadvantage in deleting a file as you are left with no options.
You have done the right thing, 'first do no harm' don't delete, send virus to the chest and investigate.
You don't say what the file name was nor do you say what your OS is (both of which can help us to help you) ?
avast is exercising extreme care when the detection is in a system folder.
They aren't wise to avast's repair function - Trojans generally can't be repaired (either by the VRDB or avast virus cleaner), because the entire content of the file is malware, so it is either move to chest or delete, move to the chest being the best option (first do no harm). When a file is in the chest it can't do any harm and you can investigate the infected warning.
The VRDB only protects certain files, mainly .exe files, it doesn't protect data files or all files, it is not a back-up program, so there are going to be many occasions where repair won't be an option.
Only true virus infection can be repaired, e.g. when a virus infects a file it adds a small part to it, provided that file is one that avast's VRDB would monitor and you have run the VRDB, then it may be possible to repair the file to its uninfected state.
However, for the most part so called viruses, trojans (adware/spyware/malware, etc.) can't be repaired because the complete content of the file is malicious.
