Often times when clients are thinking of replacing their carpet with another surface (ie. hardwood, vinyl plank, cork etc.) the thought is that the carpet and underlay can simply be removed and the new floor installed. Rarely if ever is floor Installation ever that simple.
The primary concern for installation of anything other than carpet is the condition of the subfloor underneath the carpet and pad. By it’s very nature, carpet and pad is very forgiving and hides a lot of imperfections of the sub-floor.
All sub-floors are flat… but not all sub-floors are level. According to industry standards, the maximum tolerance for deviation of a sub-floor over the span of 8-10 feet is 3/16 of an inch. Exceeding this will require preparation to some degree, low areas will require some sort of building up, high areas will have to be ground down if possible. If an installed floor fails due to lack of sub-floor preparation, this gives the manufacturer the option to void any and all warranties for their product.
The other thing to consider when going from carpet & underlay to a hard surface, is the profile change that usually happens. Carpet pile and underlay are typically thicker than the floor being installed. 99% of the time the baseboards will have to come off and re-installed. So when the baseboard is re-installed it will have dropped in height, so some touch up painting will most likely be required.