Insulin initiates glucose transport into tissues (muscle, adipose, etc) via GLUT-4, a intracellular glucose transporter. IGF-1 has a much weaker action on GLUT-4 compared to insulin.
Anabolic Pump/P-Slin have actives that claim to stimulate GLUT-4 without the need for greater insulin levels. Obviously you can see the certain benefits of this, especially since USPLabs claims that GLUT-4 stimulation does not occur in adipose tissue via these supplements, thus maximal uptake occurs in muscle and not fat.
Also, there are other actions that are different between Insulin and IGF-1 on amino acid transport for example. Here is a related excerpt:
Intracellular Organization of Insulin Signaling and GLUT4 TranslocationIGF-1 and insulin both do very similar things: they both attach to receptors of muscle cells. The receptors are very similar. These receptors are part of the cell membrane structure. GH and insulin both increase the cellular membrane permeability of certain amino acids, to thus facilitate the transfer of those amino acids into the muscle cells into the sarco-plasm.
The amino acids that insulin facilitates to cross are different than the amino acids that IGF-1 helps to cross. The entire array of both of them combined is what is necessary for "proteo-genesis" (new protein for muscles). It is like a double key system in a bank safe: you need both keys, or you can't open the safe. You need ALL the amino acids that IGF-1 helps to cross AND all the amino acids that insulin helps to cross, or you can't have proteo-genesis.
High IGF-1 with low insulin has no anabolic effect because to have new proteo-genesis you need ALL the amino acids helped across by IGF-1 AND of insulin. Low IGF-1 and high insulin also does not help to build muscle because IGF-1 is missing, so the amino acid array is incomplete.
The study below has a great table/chart of comparisons at the end.
A SITUATION DETERMINED MODEL OF THE BODY METABOLISM:
ROLES OF IGF-1 AND INSULIN DEPENDENT GLUT 4