It may be argued that upward step mashes are not necessary with 
the 2 row Klages malt which a majority of American homebrewers and 
craft brewers use and their base malt, but the addition of a protein 
rest with these malts is very beneficial.  American 2 row Klages malt 
has been developed by the barley growers and maltsters to conform to 
the specifications of the major Mega-breweries in the United States.  
One of its characteristics is that it has a very high protein content 
compared to other kinds of base malts.  While this is not a problem for 
the Mega- breweries, it is for the homebrewer.   Because Mega-breweries 
use an extremely high proportion of grist which is corn and rice and is 
extremely low in protein content, the overall protein content of the 
mash remains low in spite of the high protein content of the malted 
barley.  The same grain in the hands of a homebrewer is in the range of 
80% of the grist which changes the ratio significantly.  Therefore, it 
can be argued that homebrewers can benefit significantly by a protein 
rest and one method of getting one is to use an upward step mash.

        The value of a step mash is explained by George Fix in a 
communique in the HomeBrew Digest.  "The value of the rest at 40C 
[104F] can not be understated. The rise in SG in this mash is almost 3 
times faster than what I get when this rest is omitted. The final mash 
yield is ~20 % higher.  Clearly there is a lot of favorable activity 
going on including preparation of the enzyme systems, beta glucanase 
activity, and highly favorable enzymatically assisted grain 
liquefaction."




     Even ignoring a protein rest, one can argue that upward step 
mashes provide for more control over the composition of the resulting 
wort with respect to the ratio of fermentable sugars to unfermentable 
sugars.  Yes, it is possible to choose a single temperature mash at 
which both alpah and beta amylase  are working and by varying that 
temperature slightly, it would be possible to favor one over the other, 
thereby controlling the resulting fermentables/unfermentables ratio.  
However, by mashing at a lower temperature more favorable to beta 
amylase for a short time and then raising the temperature beyond the 
temperature favorable to the beta, the alpha amylase can be given a 
chance to finish the starch conversion into longer unfermentable sugar 
chains.  By favoring alpha amylase in a later stage of the mash, the 
proportion can be better controlled.  "The % fermentability as 
determined by a liter sized forced fermentation at 30C usually gives an 
ADF near 79% (RDF = 65%).  This means that FG limit is 1.011. The ale 
strain that I am using does not completely ferment maltotriose, so I 
usually wind up a 1.012 to 1.013 in this context. The ADF is greatly 
influenced by the times spent at 60 and 70C. E.g., 15 mins. at 60 
followed by 45 mins at 70 will typically drop the ADF into the low 70s. 
The reverse will increase it into the mid 80s. For my ale strain 
spending at least 15 mins. at 60C is crucial for it greatly increases 
the maltose/maltotriose ratio."