Want to try out new software but also keep your system clean of packages that you do not use? Unless you keep good track of everything you install for a trial, you are likely to leave some unwanted packages on your system at some stage. Not that they generally do anything apart from take disk space (at least on Arch Linux), until one day when you are doing an update and you think “What is that package doing on my system?”.
One way I have found to keep track of packages you want to temporarily install is to have a sort of secondary package management system within the main pacman database. This is achieved through abuse of the dependency tracking features of pacman. Any package that is to be installed for a temporary period get installed with the --asdep flag. This tells pacman that the package is a dependency. Given no other package depends on it, it is what is commonly referred to as an “orphan” package and can be listed using pacman -Qtd. Currently on my system I have:
$ pacman -Qtd
When I no longer want these packages on my system, they will be uninstalled in the standard way (pacman -Rs pkg). If I decide to keep the package, I can change the pacman database entry using the little known -D/--database flag. E.g. pacman -D --asexplicit vlc will change the install reason for the vlc package from being “Installed as a dependency for another package” to “Explicitly installed”. It will no longer be listed as an orphan, effectively taking it out of this secondary pacman management system inserting it into the main one.