As a rule of thumb, increasing the number of disks in an array will increase disk IO performance, when compared to a single disk (although the real benefit may be small).
RAID0 works by stripping data to the array. When writing to disk IO is split up into segments (the stripe size) and written to two (or more) disks concurrently, thus increasing write IO. When this data is read from the disk, it once again reads from multiple disks, increasing read IO. There are no RAID calculations taking place, thus implementing RAID 0 incurs no RAID performance penalty.
RAID1 works by creating a mirror of one (or more) disks on another disk. When writing to disk, IO is simultaneously written to two disks (based on stripe size). A write operation therefore requires a RAID calculation, and is why some people consider RAID1 to have "slow" writes (the actual impact is minimal). When reading from a RAID1 array, the controller is aware that both disks contain data and, if the OS supports split reads (most do), can therefore read at speeds similar to RAID0. RAID1 therefore has write speeds similar to a single disk, and read speeds similar to RAID0.
RAID10/01 (or 1+0, or 0+1), is a striped, mirrored disk; or mirrored, striped disk, i.e. two disks are striped (for performance), and then each disk in the striped pair mirrored (for redundancy). This is the fastest type of RAID generally used, and also uses the most disks (minimum of four).
WRT to increasing the performance by using RAID, you have to consider three things:
The type of IO (Read/Write);
the nature of the IO (Sequential/Random);
and the the size of IO (small files, large files).
When considering RAID it is also important to understand the importance of the RAID controller. A hardware RAID solution is faster than software RAID (on board RAID is not hardware RAID). Certain IO operations benefit more from having large cache (some storage units have 1TB!), than the underlying disk system. The average on-board fake-raid controller has no cache which further reduces any possible increases in performance....
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But, essentially, RAID/Disk IO is a complex beast and there is 99% chance that you will see absolutely zero noticeable improvement in performance from implementing RAID0.