Advantages of standard diameter arrows (6.5mm/.244.246" inside diameter) are that they're widely available, relatively inexpensive, and their inserts are simple, strong, and easy to install. Medium diameter arrows (6mm/.224-.234" ID) have similar benefits but aren't as readily available (only Black Eagle and Easton offer them as far as I know).
Standard and medium diameter arrows use strong, simple inserts that sit entirely inside the arrow except for a small lip/flange that covers the front end of the shaft. The entire broadhead/field point shank (both the threaded and unthreaded portions) sits inside these inserts and thus inside the arrow shaft, which makes for a very strong front end to the arrow. These inserts are also very easy to install because the flange serves as a depth stop...just apply adhesive and shove them in until you hit the front end of the shaft.
When you go smaller than medium diameter, inserts get more complicated and expensive and can become a significant weak point in the arrow. For small diameter arrows (5mm/.204" ID) you have three insert choices:
- Hidden insert (often abbreviated as "HIT")
- Half-out (often mistakenly called an outsert)
- Flanged Deep Six insert (rarely used and few folks know these exist)
I personally avoid all types of half-outs because they're inherently weaker than the other two options. A half-out keeps the threaded portion of the head/point shank inside the arrow shaft, but the unthreaded portion extends out in front of the shaft. That extra length sticking out in front of the shaft amplifies the pressure exerted on the front end of the arrow when you hit something at an angle and is more likely to bend or break. A HIT is a flange-less insert that sits fully inside the shaft and keeps the entire head/point shank inside the shaft. HIT's are slightly trickier to install and require the use of a specific tool to get the depth correct, but they're inherently stronger than a half-out. Option 3 is a scaled down version of a standard diameter flanged insert with "Deep Six" (6-40) threads instead of typical 8-32 threads. These are simple and strong inserts, but you have to use heads/points with Deep Six threads. Very few manufacturers offer Deep Six heads (Iron Will, QAD, maybe a few others) so your options are very limited.
You didn't ask about micro diameter arrows (4mm/.166" ID), so I won't go down that rabbit hole...suffice it to say the insert conundrum gets even worse.
The advantage (in theory) of a smaller diameter arrow is reduced wind drift due to the arrow's reduced surface area. However, IMO the wind's effect on the shooter's ability to aim is far more impactful than the wind's effect on the arrow in flight (especially at trad distances).