1) Higher spotting scope powers will affect the image brightness by scattering your incoming light over a larger aperture area.
2) As you increase your power, you end up decreasing your field of view. This means it gets harder finding your subject in the lens and keeping it centered.
3) More power can cause some image degradation.
This doesn't mean you can't enjoy the power that is available, it just means you should consider buying a spotting scope based on the type of viewing you plan on doing.
If simple treks in search of birds or animals is your preference, a 50mm - 60mm spotting scope will do just fine. If you want to see eagles nesting on the side of mountains, then you will need to get real close with a spotting scope in the range of 80mm - 127mm.
TRIPODS - THE SPOTTING SCOPE'S BEST FRIEND
Without a solid tripod, your scope won't have a leg to stand on - literally! Let's face it, nothing is more frustrating than capturing a great visual experience only to tire out from hand-holding a spotting scope. Put an end to vibrating, jittery motion with a well-built tripod.
There are many choices on the market but you will find that owning a tripod with a removeable "shoe" is a real time-saver. This shoe or metal plate, is the fastening mechanism which holds the spotting scope firmly on top of the tripod. You can leave it attached to your scope permanently and appreciate that it basically clicks and clips on quickly to a tripod that has this feature.
A key item to remember is that your tripod should be lightweight. You're looking for something that will "telescope" from 6 feet high down to 2 ft. in order to have some practical portability - especially when hiking long distances. Consider that a solid tripod isn't a function of weight but rather of having a well designed spotting scope accessory that does what it's built for - support. The right spotting scope tripod should be determined by the size of the scope you hope to buy.