Is there any point using a .5mm needle for microneedling or better to use 1.0 mm or higher for better results?

at home . use of 0.5mm is . great, in . office 0.75-1.5 . is sufficient.  i suggest weekly with 0.5mm and monthly with 1.5mm. 
For facial rejuvenation I would suggest a combination approach of :

1) skin care with products and PRP/microneedling
2) PDT light therapy few times a month with growth factors
3) laser treatments like clear and brilliant regularly and a few times a year Fraxel, Viva, Co2/Erbium
4) Sculptra injections a few times a year for collagen production with fillers like juvederm/restylane/belotero/radiesse/bellafill
5) thermage/ultherapy for yearly skin tightening with or without PDO or cone based instalift threads for lifting
6) botox every 2-3 months to stop movement lines and prevent lines at rest

I always start and finish with the 0.5mm to initially get the growth factors and serums into the skin so the deeper settings can push it down into the dermis. I also finish with 0.5mm to blend all areas together for a smoother finish. I agree that a 0.5mm alone won't do much but it definitely has its uses when combined with deeper settings. Hope this helps!Johnson C. Lee, MD
Board-Certified Plastic Surgeon
@drjohnsonlee