It goes without asking that first you have to set up any Linux or FreeBSD on your system, preferable at least 2 different kinds, all tested and working prior wiping Windoze.
E.g. I have via my internal hard disk: One Puppy, One Tiny Core, and several Porteus. All tested, all working. Usually I only boot into Porteus, but Puppy and Tiny Core are such small live systems that in my book it never hurts to keep these around, just in case.
Of course, when the main MBR got corrupted, overwritten, or whatnot, none of these would boot, but then neither would any WIndoze unless your PC has a optical drive (subnotebooks nowadays come without any) and a working bootable Windoze CD-ISO or DVD-ISO at hand. And the later must more often than not created manually by the user since most Windoze-preinstalled PCs for some years now get shipped with SM-Witless pre-installed on the hard drive only but no bootable rescue and restore CD or DVD-disc given to the paying customer.
Like I said: my recommendation getting rid of windows only goes without saying is only true when
● the user no longer needs it because at least one Linux can do all the work he needs done
● the user has at least 2 different Linux or FreeBSD systems installed on the internal hard drive, better 3, all tested at least once per alternative
● the user has a bootable rescue system: either via CD-ROM or via USB thumbdrive that has at least gparted and all needed fsck and fdisk / cfdisk / sfdisk. And these external rescue systems all tested as well.