2021 7,500 active satellites in LEO as of September 2021
There are at least 128 million pieces of debris in LEO. Of those, around 34,000 are over 4 inches (10 centimeters), according to the There are already at least 128 million pieces of debris in LEO. Of those, around 34,000 are over 4 inches (10 centimeters), according to the Natural History Museum in London, LiveScience

Almost half are inactive GeospacialWorld

Type	Altitude (mi)	Speed MPH	period	use
Clouds	1-4
Commercial Airplanes	7	570
SR-71 Blackbird	15	2,275
Highest manned baloon	21
SpaceShipOne rocket plane	70	2,375
Low Earth Orbit LEO	50-1200	17,000	90 min	weather, reconnaissance (spy) or Earth-mapping
Space Shuttle	190 - 330	17,000
International Space Station (ISS)	173 - 286		92 min
Hubble Telescope	370
Medium Earth Orbit MEO	1,200-12,000		2 - 12 hrs	Navigation,
GPS Satellites Semi-Synchronous Orbit SSO	12,644		12 hrs
Geostationary orbit High Earth Orbit HEO	23,300	6,870	24 hrs	telecommunications, Satellite TV
Geostationary orbit High Earth Orbit HEO	23,300	6,870	24 hrs	telecommunications, Satellite TV
James Webb Space Telescope	1 million		365 days	Target launch date is 2018. It is 4 times the distance of the moon at a Lagrange point relative to the sun and earth so they stay in the same positions relative to each other. Studies the study the Universe in infrared light. See The James Webb Space Telescope Science
Moon	225,622 - 252,088		27 days

The earth's diameter is 7,926 miles.

Large image at Wikipedia

The advantage of LEO's is lower power required for radio transmitters and more detailed viewing for weather and reconnaissance.
There is also less time delay.
The disadvantage is the small fast moving footprint for ground radio reception.
You can only get direct radio signals for about 10 minutes for the International Space Station (ISS) while a given GPS satellite will be accessible for 5-10 hours.
In some cases constellations of multiple satellites are required.
Some satellites (e.g. Search and Rescue LEOSAR) have a wider angle of coverage for a larger footprint.

Polar Earth Orbits can be positioned at different altitudes above the Earth's surface depending on their uses. Polar orbit satellites are most often used as weather, reconnaissance (spy) or Earth-mapping satellites. They are typically at LEO altitudes.

GPS satellites are between 6,000 and a Semi-Synchronous Orbit with a period of 12 hrs at 12,644 mi.

Objects in LEO encounter atmospheric drag in the form of gases in the thermosphere (approximately 80-500 km up) or exosphere (approximately 500 km and up).

The Joint Space Operations Center, part of United States Strategic Command (formerly the United States Space Command), currently tracks more than 8,500 objects larger than 10 cm in LEO,[4] however a limited Arecibo Observatory study suggested there could be about one million objects larger than 2 millimeters,[5] which are too small to be seen from the ground.
See Space junk by wayne@sparkleberrysprings.com

Glossary:
Satellite Orbits
OSDPD - Office of Satellite Data Processing and Distribution at NOAA
Cospas-Sarsat is an international satellite-based search and rescue (SAR) distress alert detection and information distribution system, established by Canada, France, the United States, and the former Soviet Union in 1979. Links:
Orbits at NASA.gov
Satellite - Software: Satellite tracking
Live Real Time Satellite And Space Shuttle Tracking And Predictions
X XM & Sirius in Orbit
GPS in technology