Hammer drills are very versatile tools. The basic hammer drill has a switch which disables the hammering action, turning it into a normal drill. Cordless hammer drills can generally be used as screwdrivers as well. But you also have much more powerful hammer drills, the rotary hammer is the right tool for drilling hard materials, such as concrete. Here is a short hammer drill overview.
For most DIY tasks the standard hammer drill is the best choice. The hammering action makes it possible to drill in hard materials. And you can disable the hammering action when you don’t need it. The hammering action generally damages softer materials. So if you are going to drill a hole in a concrete wall which is covered by a layer of plaster, you need to be careful. The hammering action will damage the plaster. The solution is to drill without the hammering action until you reach the concrete behind the plaster, then you enable the hammering action.
In most cases, a cordless drill is more convenient than a corded drill. But if you are going to use the hammering action a lot, you may prefer a corded hammer drill. The hammering action quickly drains the battery.
Of course, you also need drill bits that are meant for masonry drilling. Standard drill bits will quickly break if you use them in hard materials. But note that the rotary hammer has its own bits.
If you are going to do a lot of drilling in hard materials, you may prefer to use the more powerful rotary hammer rather than a normal hammer drill. It has a piston mechanism that does the hammering action. This makes the hammering action of the rotary hammer much more powerful, letting you drill holes much faster. But you can’t use drill bits meant for hammer drill. The powerful action of a rotary hammer requires special bits that lock tighter into the hammer. Ordinary bits are too smooth, they will be pounded loose very quickly.
Rotary hammers are too big and clumsy to be used in soft materials. But you can disable the rotary action and turn the rotary hammer into small destruction hammer, which can be used for chipping jobs.
The combination hammer is a combination of rotary hammer and demolition hammer. You can use them both for drilling concrete as well as for chiseling and chipping. Of course, they are not as powerful as standard demolition hammers but you get good value for your money. Demolition hammers are similar to rotary hammers but they lack the rotary action needed for drilling. It is the tool for demolishing concrete and masonry.