Stock vs diluted solution

Last night I was developing a few different films in Microphen and noticed some don't have a time recommendation for anything but an undiluted solution (stock, 1+0)
I had been developing HP5 in 1+1 mostly for economical purposes but then I started wondering, all other things being equal (temperature, agitation etc) what difference is there between using a stock or a diluted solution ?

How does it affect contrast, shadows/highlights, grain ?

Microphen isn't a general purpose developer though, it's a compensating developer for push processing.

Michael is right Microphen is considered a general purpose developer and is marketed as such. In general there is a some overlap in the designations for developers and a developer's character can be effected by usage such as dilution.

Oh that's interesting thanks guys. So out of curiosity, what would make a developer compensating that isn't present in Microphen ?

When Ilford began substituting Phenidone for Metol in their commercial formulae in the 1950's they experimented with a PQ version of ID-11/D76 and noticed a slight increase in effective film speed, eventually they released Autophen a photofinishing PQ variant of ID-11 for large scale commercial replenished use.

They then went a step further releasing Microphen (ID-68) which gives a greater increase in effective film speed partially due to dropping the Sulphite level which results in tighter more apparent grain. There's nothing particularly new Adox Borax MQ, Agfa 44 (Agfa Ansco/GAF 17) both MQ developers are 1/3 of a stop faster than D76/ID-11 and a aPQ equivalent adds another 1/3 of a stop.

Dropping the Sulphite increases sharpness, gives grain a more pronounced structure as you lose the solvency effects.

Ian