When it comes to air quality in residential homes, a Merv rating of 17-20 is rarely necessary. A Merv rating of 13-16 is considered hospital-level air quality, so it's unlikely that your home will need more than that. Of course, higher MERV filters are not a bad thing. It's important to ensure that the rest of the system is configured to handle the increased restriction that filters create.
Filters with higher Merv ratings capture higher percentages of particles, as well as smaller particles. MERV-13 is practically where you want to be. The higher the MERV rating of a filter, the less dust particles and other contaminants can pass through it. Low-efficiency filters are generally within MERV 1-4 and high-efficiency filters are MERV 13 and beyond.
High MERV air filters that contain pleats create more surface area for air to blow, which can improve airflow and reduce strain on the system. Technology for HVAC units has progressed since then and most modern units in recent years should be able to have a MERV 8 filter at least. With all due respect Allison, questioned the need for the MERV 13 leak. When you have a Merv filter 13 and higher, it's more similar to the material you'd find in an n95 dust mask.
The MERV scale is not linear; the difference between a MERV 6 and a MERV 8 is almost double in the percentage of particles captured. As an HVAC professional for more than 40 years, I have seen dozens of systems destroyed by the use of highly restrictive MERV filters. It's important to replace dirty filters often enough, which can be a week or two, depending on the MERV rating, the effective area of the filter, and how many particles enter in his house. Air filters with a MERV of one to four are effective at removing large particles such as carpet fibers, airborne paint droplets, and sanding dust, but they cannot help with contaminants such as hairspray, mold spores, or even flour that could have escaped from the mixer.
Not all filters have a Merv rating; many of them are purchased at large stores. In conclusion, there is no price for peace of mind and if you feel that a high MERV filter would provide it, you should do so with the caveat that you should replace dirty filters often enough.